Aircraft manufacturers continuously attempt to improve aircraft performance by reducing both weight and manufacturing costs while maintaining or improving structural strength. One well-known method for increasing aircraft performance is to reduce airframe weight through the use of materials such as composites having relatively high strength-to-weight and stiffness-to-weight ratios. Composite materials are generally described as being materials that include reinforcing fibers, such as carbon fibers, embedded in a polymeric matrix, such as an epoxy resin.
Generally, load bearing structures of an aircraft comprise longitudinal stiffening elements called stringer members and circumferential stiffening elements called frame members. These stringer members and frame members are positioned on the skin panel of the fuselage of an aircraft by intersecting each other in order to form a grate structure. The skin panel, the stringer members and the frame members are usually made of the above-mentioned fiber reinforced composite materials or of aluminum.
In the intersection areas in which the stringer members and frame members are intersecting each other, one stiffening element runs across the other stiffening element. Additional elements like clips or shear webs are used in order to attach one stiffening element to the skin and the other stiffening element at these intersection areas.
Document U.S. Pat. No. 8,079,549 B2 describes structural panels for use in manufacturing fuselage bodies wherein a monolithic integrated structural panel is configured to include a skin, an array of stringer members and an array of frame members which are preferably arranged in a mutually orthogonal layout. The junctions of the frame and stringer members are fabricated from several single preformed modular junction elements. Additional bridge elements are provided for realizing the intersection areas.